Streptococcus sanguis and S. mutans were grown in the continuous mode both singly and in coculture. The results showed that S. sanguis had a higher affinity for glucose used as a limiting energy source than S. mutans. S. mutans, however, appeared to produce an inhibitor to S. sanguis. The inhibition of S. sanguis by S. mutans was demonstrated by growth of the organisms in a two stage continuous culture and in cell free media following the growth of S. mutans. The basic growth parameters of some S. mutans isolates with altered caries potential and altered growth on sucrose have been calculated from continuous cultures limited by glucose and sucrose. Studies of the chemical composition of oral bacteria grown in highly controlled conditions of pH and nutrient composition towards an understanding of the antigenic determinant of the salivary IgA response towards S. mutans have continued.